The invention relates to a method for actuating a reversible vehicle occupant protection means in a motor vehicle.
In contemporary motor vehicles, restraint means such as seatbelts and airbags which can be actuated are used to alleviate the consequences of accidents for a vehicle occupant. Methods for actuating these restraint means in a motor vehicle are known from practice and from a large number of publications.
In addition to the current restraint means such as airbags and safety belts with seatbelt pretensioners there are a series of further vehicle occupant protection devices which can be actuated and which bring about a restraining effect and/or an energy-absorbing effect in order to protect a vehicle occupant when there is a collision. Examples of such vehicle occupant protection devices are movable impact bodies, cushions and headrests whose size, hardness, shape and position can be changed by an actuation devices. In addition to these vehicle occupant protection devices, in order to alleviate the severity of accidents it is possible to provide further protection devices which can be actuated and which alleviate the consequences of accidents for a vehicle occupant by virtue of the fact that the occupant is positioned, that is to say he is moved into a position which is favorable with respect to an accident. The devices for positioning the vehicle occupant are, for example, an electric seat adjustment device, a headrest adjustment device, a seatbelt pretensioner and a movable cushion element.
In order to alleviate the consequences of accidents in motor vehicles it is also possible to provide protection devices which can be actuated and which also serve the purpose of protecting other parties in collision, for example protecting pedestrians and cyclists. Examples of this are adjustable engine hoods, movable fenders and impact elements on the outer skin of a vehicle which have an adjustable hardness. Further protection devices which can be actuated are the ride level control devices and the braking and steering system by means of which an impact can be optimized in the direction of a lower degree of severity of injury for vehicle occupants and/or other parties in collisions. These devices are not understood below as vehicle occupant protection devices in the sense of the present invention.
When protection devices for alleviating the consequences of accidents in road traffic are actuated, it is possible to distinguish between preventive measures, which are taken before an accident, and acute measures which are taken after an accident has been detected. The invention relates to actuating protection devices as a preventive measure.
DE 19524358 C1 discloses that the hazard warning light system, an impact protection device and a seatbelt pretensioner are actuated when there are abrupt full braking operations, taking into account the speed of the vehicle. It is known to trigger safety devices with a preventive effect during a panic braking operation. For example, the seatbelt is preventively tightened during a panic braking operation which is detected.
U.S. Pat. No. 4,258,931 describes a reversible protection system in the form of an airbag for a motor vehicle which is actuated in anticipation of a collision as a function of the brake pressure. For this purpose, a pressure sensor which senses the hydraulic pressure and by means of which an emergency situation is inferred is provided in the hydraulic circuit of the brake system In the case of an emergency situation, a valve is actuated in order to cause the airbag to be filled. If the emergency situation does not lead to an accident, the driver vents the airbag manually using a switch. If an accident takes place without an emergency situation having been detected in anticipation of the accident, the airbag is triggered by means of accident-detecting sensors.
The genus-forming DE 10005010 A1 discloses a method for actuating a reversible vehicle occupant protection system in a motor vehicle, in which case driving state data is sensed using a sensor system. The driving state data is monitored with respect to a state of emergency braking, and when the state of emergency braking is determined the vehicle occupant system is triggered before the collision time and moved into an effective position. In addition, this genus-forming document discloses that a critical traffic situation is determined from the driving state data relating to the steering angle, wheel speed, yaw rate and acceleration.
DE 19708508 which relates to a method for sensing driving state data discloses that the state of oversteering is determined by means of an evaluation of the altitude angle.
Furthermore, DE 4200061 A1, which is also concerned with determining driving state data, discloses that the altitude angle is determined from the wheel speeds, the yaw rate and the lateral acceleration.
The object of the invention is to reduce the consequences of accidents in road traffic.
An advantage of the method according to the invention is that many of the accident situations are already detected before the collision by using the sensor system which is already present in the vehicle, without making additional use of ambient data, and that on the basis of this the safety of the vehicle occupant(s) is significantly increased by actuating reversible protection systems.
The sensor system for sensing driving state data comprises, for example, a steering angle sensor, a pedal travel sensor, a brake pressure sensor, wheel speed sensors, acceleration sensors and a yaw rate sensor. The steering angle sensor senses the steering angle at the steering wheel, this steering angle constituting, as does the pedal travel, a setpoint variable of the driving operation. In contrast, for example the sensed accelerations, the yaw rate and the wheel speeds are actual variables of the driving operation. A reversible vehicle occupant protection device is a device whose purpose is to alleviate the stress on a motor vehicle occupant in the case of a collision, the protection device being repeatedly moved from the initial state into an effective state, and can be returned from the effective state into its initial state.
Emergency braking occurs if a braking process takes place with at least one feature which indicates a hazardous or emergency situation. This is the case if this feature (these features) lies (lie) significantly outside a predefinable value range. The state of emergency braking is determined by using at least one of the parameters of the brake pressure, speed of the activation of the brake pedal and speed of the retraction of the accelerator pedal to evaluate the braking operation.
As an alternative to an emergency braking operation which is brought about by the driver, emergency braking can be carried out in an automated fashion on the basis of the sensing of the environment. A signal which indicates that automated emergency braking, for example the control signal for the triggering of the emergency braking operation, can also be used to carry out the method according to the invention.
The state of understeering of the vehicle signifies that the radius of the setpoint path of the vehicle which is predefined by the steering angle is smaller than the radius of the path which is actually traveled through by the vehicle. In contrast, oversteering of the vehicle means that the radius of the setpoint path which is predefined by the steering angle is larger than the radius of the path which is actually traveled through. The setpoint path which is predefined by the steering angle is to be understood as the trajectory of the vehicle, which comes about when the vehicle travels with the steering angle to be considered and at such a low speed that the lateral forces can be ignored in comparison with the longitudinal forces. The driving state data can be used to determine the states of understeering and oversteering.
The data processing device continuously checks whether one of the states of emergency braking, oversteering or understeering is present. If this is the case, the reversible vehicle occupant protection system is actuated, it being possible to adapt the triggering speed, the actuation speed, the hardness and the direction of effect as a function of the states of emergency braking, of oversteering and of understeering. In particular, the actuation of the vehicle occupant protection device when more than one of the states of emergency braking, of understeering and of oversteering are simultaneously present is adapted to a combined hazard, for which it is possible to provide an additional evaluation algorithm.
In addition, the direction from which a maximum hazard is to be expected is determined by means of the states of emergency braking, of oversteering and of understeering. The vehicle occupant protection system is actuated in accordance with the determined direction of the hazard in such a way that the protective effect is provided in accordance with the direction of maximum hazard. Considering the states of emergency braking, of oversteering and of understeering together it is possible, when more than one state which indicates a hazard is present to actuate the protection system in such a way that the stress on the vehicle occupant in the case of an accident is as low as possible.
In one development of the invention, the reversible vehicle occupant protection system is actuated only if the vehicle is at or above a minimum speed. This has the advantage that it is possible to prevent actuation of the vehicle occupant protection systems at low speeds. It may be desired not to actuate the vehicle occupant protection systems below a predefinable speed as, at a low speed, a hazard to the vehicle occupants which may be detected by means of the driving state data is negligibly small.
In one advantageous configuration of the method, the state of emergency braking is detected by means of an intervention into the driving dynamics which is performed by a brake boosting system. This brake boosting system itself evaluates driving state variables in order to intervene in the driving dynamics as a function of the evaluation result. The intervention of the brake boosting system in the driving dynamics takes place by transmitting control signals to the actuation devices which influence the driving dynamics. These control signals of the brake boosting system can be used to detect the emergency braking operation. As an alternative to the control signals it is possible to use a different information signal which is transmitted by the brake boosting system to a data bus in order to detect the state of emergency braking. An advantage of this configuration of the method is that an emergency braking operation is detected with particularly little expenditure. On the other hand it is necessary to accept that triggering of the protection systems is associated with the algorithm of the brake boosting system.
In one further configuration of the method, the control signal of the brake light switch is used to check the plausibility of the emergency braking operation. This signal is frequently made available on a data bus in the vehicle so that no additional expenditure on cabling comes about. An advantage of the redundancy which is achieved by means of this development of the method with respect to the detection of an emergency braking operation is that the reliability of the decision when a reversible protection system is actuated is increased.
In one configuration of the method, the states of understeering and oversteering are determined by virtue of the fact that the difference formed between an angle which describes an actual change in the driving direction and the steering angle is evaluated. This evaluation may comprise a simple threshold value interrogation, the threshold value being permanently predefinable, or the threshold value can be adapted as a function of other parameters, for example the properties of the road or the loading of the vehicle. The states of oversteering and understeering can also be determined using chronologically preceding values of the travel-describing angle and of the steering angle. By means of the previous values of the angles which are determined it is possible to form the difference between two angles as a function of time and subject it to an evaluation. For example, the calculated difference in angles can be integrated over a predefinable time period, or the gradient of the difference in angles is evaluated.
The angle which describes a change in the actual direction of travel can be determined from different parameter sets. This may be used to check the plausibility of the determination of a state which leads to the triggering of a protection system. The reliability which is achieved by means of a redundant determination of a triggering state permits the protection system to be actuated at lower triggering thresholds, and thus at an earlier time. Parameter sets which can be used to determine the state of understeering may be, for example, the wheel speeds, the lateral acceleration and the wheel base, or in another example the wheel speeds, the yaw rate and the wheel base. Both parameter sets are advantageously available on a data bus system in modern vehicles. Instead of the wheel speed it is also possible to use the vehicle speed directly, it being possible to determine the vehicle speed from the wheel speeds.
With respect to the determination of the state of oversteering it has been found that the altitude angle is a variable which is suitable for this and which directly characterizes oversteering. The altitude angle may be determined from the available parameter set of the yaw rate, lateral acceleration and one of the parameters of the wheel speeds or vehicle speed, it being in turn possible to determine the vehicle speed from the wheel speeds.
In order to additionally protect against the state of oversteering, a setpoint yaw rate is determined which is calculated from the vehicle speed and the steering angle. If the difference formed between the setpoint yaw rate and yaw rate exceeds a predefinable threshold, the state of oversteering is also inferred.
In one advantageous configuration of the method, the protection system comprises an electric seat adjustment device and/or an electric adjustment device for orifices in the vehicle and/or a reversible seatbelt pretensioner and/or an electrically adjustable impact protection device. An electric seat adjustment device and electric adjustment devices for orifices in the vehicle, for example the electrically adjustable sunroof and electrically adjustable window lifters are present at least to a certain extent in contemporary vehicles and can additionally be used for preconditioning the vehicle occupants or the vehicle at low expenditure. All the electrically adjustable protection systems have the advantage that the energy supply is provided easily via the vehicle's on-board power system, in particular electromotive drives easily permit the reversibility of the protection systems. As a result, it is possible to trigger the protection systems, while taking into account their effect on the driver and vehicle occupants, even if a hazardous situation is determined which will not lead to a collision with a high degree of certainty but merely with a certain, predefinable probability. The method according to the invention has the effect of detecting such a hazardous situation, the intention being that in a simple embodiment the method can already be carried out in contemporary vehicles without additional sensor systems and without additional actuator systems.